Water washable dye penetrant composition and method of application

ABSTRACT

Water washable substantially biodegradable dye penetrant composition for use in non-destructive dye penetrant inspection of parts for locating cracks and flaws therein, consisting essentially of an organic dye, preferably a fluorescent dye, a carrier or solvent for said dye in the form of certain ethoxylated linear alcohols, particularly the biodegradable nonionic surfactants comprised of ethoxylates of a mixture of secondary alcohols having linear alkyl chains of from 11 to 15 carbon atoms, and an average of from 3 to 12 moles of ethylene oxide, and glycol monobutyl ether for thinning the dye penetrant solution substantially without affecting the sensitivity of the penetrant or its biodegradability, and facilitating application of the liquid dye penetrant composition by spraying to the surface of an object or part to be inspected. In the method of application of the dye penetrant composition, such composition is applied to the surface of an object containing cracks and flaws, water is applied to the surface of the object, preferentially removing the glycol monobutyl ether vehicle or carrier, and almost immediately thereafter removing the remaining dye penetrant distributed on the surface, both the removal of the glycol ether component and the remaining dye penetrant occuring in the same washing operation. The part is then inspected under appropriate lighting conditions such as fluorescent or black light, to obtain colored traces from the dye penetrant remaining in the cracks and flaws.

This application is a continuation-in-part of my copending applicationsSer. No. 444,433, filed Feb. 21, 1974, now Pat. No. 3,915,886 and Ser.No. 521,730, filed Nov. 7, 1974, now Pat. No. 3,939,092.

BACKGROUND OF THE INVENTION

This invention relates to an improved biodegradable dye penetrantcomposition and method for non-destructively testing material specimensto locate and identify surface voids, cracks or defects, and isparticularly concerned with the provision of an improved water washablebiodegradable dye penetrant composition or solution containing aspecific relatively non-volatile solvent for thinning such waterwashable dye penetrant, such solvent being preferentially removable fromthe part surface followed by removal of excess dye penetrant, uponapplication of water to an object to which the dye penetrant compositionhas been applied, the dye penetrant composition remaining in the cracksand voids of the part having substantially the same properties as theinitial composition in the absence of such solvent, particularlysubstantially the same sensitivity, the biodegradability of the excessdye penetrant removed from the object surface being substantiallyunaffected by such solvent. The invention is also concerned with themethod of employing such thinned water washable dye penetrantcomposition in a penetrant inspection process.

In known penetrant inspection methods for rapid location and evaluationof surface flaws or cracks in test bodies or parts, a dye penetrantcomposition, preferably containing a fluorescent dye, and which willpenetrate the openings of the surface cracks or flaws in the part, isapplied to the surface of the test body, and the excess penetrantcomposition is removed from the surface of the body. A developercomposition may then be applied to the part surface, which acts as awick and causes the liquid penetrant containing the fluorescent dye,which was retained in the cracks or surface flaws, to be drawn up out ofthe surface defects by capillary action. The part is then exposed toappropriate lighting conditions, such as invisible fluorescigenouslight, and the location of the surface flaws is revealed by the emissionof visible fluorescent light by the penetrant dye which was retained inthe cracks or flaws after the penetrant composition was removed from thesurface of the part.

For best efficiency, particularly for the detection and location ofminute surface cracks and flaws, as well as intermediate size and grosscracks, it is necessary that the dye penetrant composition have highsensitivity.

Volatile type solvents are commonly employed for extending or thinningdye penetrant inspection solutions or compositions. This is done chieflyfor the purpose of lowering the viscosity of the penetrant in order toadapt it for application in spraying systems. Thus for example solventssuch as kerosene, light fuel oils, and methyl ethyl ketone, all highlyvolatile solvents, have heretofore been employed in prior art dyepenetrants. See for example U.S. Pat. No. 2,806,959.

Another reason for thinning a penetrant solution is the resultingeconomy due to the extending effect which the solvent has in thepenetrant solution. However, for this purpose, the solvent mustevaporate quickly after its application to a part surface, otherwise theproperties of the penetrant, such as fluorescence and sensitivity aregreatly reduced by the presence of a solvent which does not evaporate.Therefore, the use of volatile solvents has heretofore generally beenconsidered necessary for this purpose.

However, the use of volatile solvents in dye penetrant compositions hascertain disadvantages. Thus, the use of volatile solvents in dyepenetrants results in the evolution of fumes and solvent vapors whichare rapidly formed by the evaporating solvent.

An additional criterion has recently developed also with respect to dyepenetrant solutions and compositions. Generally, dye penetrant solutionspresently being used and containing solvents and wetting agents presenta disposal problem in that they are substantially non-biodegradable,that is, they are very difficult to decompose by bacteria in sewagedisposal plants. Hence the necessity for the development of dyepenetrant solutions and compositions which are biodegradable, that iswhich employ dye solvents and carriers which are biodegradable, and arereadily available despite the petrochemical shortage, has attainedconsiderable importance.

In my above copending applications there is disclosed a novel dyepenetrant which has improved washability and sensitivitycharacteristics, and which is biodegradable, containing as the vehiclefor the dye, certain biodegradable nonionic ethoxylated alcohols, orcombinations thereof.

In my U.S. Pat. No. 3,777,157 there is disclosed a water washable dyepenetrant composition which comprises N-methyl-2-pyrrolidone, a mixtureof a ketone and wetting agents, a fluorescent dye and glycol monobutylether which functions as a thinner for the dye penetrant composition.Although such dye penetrant composition has been found effective, it hasthe disadvantages of requiring a multiplicity of dye carriers orsolvents, with proper balance thereof necessary to provide a desiredsensitivity, and the composition is not biodegradable.

Accordingly, the main object of the present invention is the provisionof a water washable biodegradable dye penetrant solution or compositionwhich avoids the use of volatile solvents and its above noteddisadvantages, yet which can be readily applied as by spraying to a partsurface and readily removed following application of the dye penetrantto a test body, substantially without affecting the properties of thedye penetrant composition, and particularly its sensitivity andbiodegradability. An additional object is the provision of procedure forutilizing such improved water washable dye penetrant composition in adye penetrant inspection method.

DESCRIPTION OF THE INVENTION

It has been found that the above objects and advantages can beaccomplished according to the invention, and an improved water washabledye penetrant composition afforded, having good sensitivity fordetection of cracks and defects in part surfaces, and which isbiodegradable, by employing as a solvent or carrier for the dye, e.g.fluorescent dye, certain biodegradable nonionic surfactants comprised ofcertain ethoxylated linear alcohols, of the type disclosed in my abovecopending applications, separately or in admixture, and incorporatingthe relatively non-volatile solvent, glycol monobutyl ether (otherwiseknown as ethylene glycol monobutyl ether or 2-butoxy ethanol) andcommonly known as butyl Cellosolve. Such glycol monobutyl ether solventfunctions as a temporary additional carrier or extender for the dyepenetrant, and has the important property and advantage of diluting orthinning a water washable penetrant composition of the type noted above,particularly one containing a fluorescent dye, substantially withoutaffecting or changing the sensitivity of the dye penetrant in the cracksand flaws, following removal of such extender, and substantially withoutaffecting the biodegradability of the excess dye penetrant compositionremoved from the part surface, following the preferential removal of theglycol monobutyl ether component.

It has been found unexpectedly that the biodegradable dye penetrantcomposition hereof containing the biodegradable ethoxylated alcoholsurfactant essentially as sole carrier for the dye, in contrast to thedye penetrant composition of my above patent containing the entirelydifferent pyrrolidone as carrier and ketone and wetting agents, can besuccessfully thinned or extended with as much as 150% by volume, ofglycol monobutyl ether without affecting the sensitivity of theremaining dye penetrant composition following removal of the glycolmonobutyl ether, or the biodegradability of the excess dye penetrantwashed from the part surface.

It was also found unexpected that the use of glycol monobutyl ethersolvent as an extender in the dye penetrant composition of the inventioncontaining the highly water miscible ethoxylated alcohol surfactantsdescribed herein, enhances the washability of the excess dye penetrantcomposition from a part surface without removing or dislodging theentrapped dye penetrant composition from the surface defects and cracksin the part.

Thus, for detecting cracks and flaws on the surface of a part employingthe dye penetrant composition of the invention containing the glycolmonobutyl ether solvent, such dye penetrant solution is applied to thesurface of the part, and a water wash is applied to the dye penetrantcovering the surface, preferentially first removing the glycol monobutylether from the dye penetrant, and followed substantially simultaneouslyby removing or washing away of the remaining liquid dye penetrantcontaining the dye and ethoxylated alcohol surfactant vehicle,distributed on the surface. However, this is an essentially single stepwater washing operation, and the preferential removal of such glycolmonobutyl ether together with subsequent immediate removal of remainingliquid dye penetrant, both occur in a single washing operation.

The glycol monobutyl ether component is not photochemically reactive andis relatively safe to the environment. Therefore, when washedpreferentially from the surface of the object, followed by washing ofthe remaining or excess dye penetrant containing biodegradable nonionicethoxylated alcohol surfactant, the biodegradability of such penetrantafforded by the biodegradable nonionic surfactant is not adverselyaffected by the initial presence therein of glycol monobutyl ether orthe presence therein of glycol monobutyl ether following the washingoperation.

Further, as previously noted, in view of the marked difference inchemical composition of the solvent carrier in the form of theethoxylated alcohol surfactant employed in the dye penetrant compositionhereof as compared to the pyrrolidone-type carrier containing ketone andadditional wetting agents employed in the above patent, it wasunexpected to find that the glycol monobutyl ether component functionssuccessfully in the ethoxylated alcohol surfactant-containing dyepenetrant composition of the present invention as an effective extenderat high dilution, that is with a high concentration of the glycolmonobutyl ether, while at the same time not adversely affecting thesensitivity of the remaining dye penetrant composition in the cracks andflaws of the part.

The nonionic biodegradable solvents or carrier which can be employed assubstantially the sole vehicle for the dye of the dye penetrantcompositions according to the present invention are ethoxylates of amixture of linear secondary aliphatic alcohols, with the hydroxyl groupsrandomly distributed, the linear aliphatic hydrophobic portion of suchalcohols being a mixture of alkyl chains containing in the range from 10to 17 carbon atoms, preferably from 11 to 15 carbon atoms, andcontaining an average of from 3 to 12 moles of ethylene oxide.

The above preferred class of nonionic biodegradable surfactant employedas carrier for the dye penetrant of the invention is a mixture ofcompounds which can be represented by the formula: ##STR1## where n isin the range from 9 to 13, and m is an average of 3 to 12.

Although preferably each of the above-defined surfactants is formed of amixture of two or more linear alkyl hydrophobic chains ranging from C₁₁to C₁₅, as noted below, the surfactant can contain a single such chainformed from a single secondary aliphatic alcohol of the types describedbelow.

The linear alkyl hydrophobic portion of the above defined surfactant isa mixture of C₁₁ and C₁₅ linear alkyl chains, and can be derived from amixture of C₁₁ to C₁₅ aliphatic secondary alcohols, for example thesecondary undecyl, dodecyl, tridecyl, tetradecyl and pentadecylalcohols. The hydrophilic portion of the surfactant is a polyoxyethylenechain randomly attached to any carbon atom of the linear alkylhydrophobic chains, other than to the terminal carbon atoms thereof,through an ether linkage. It will accordingly be understood that thespecific carbon atom in the alkyl hydrophobic chains to which thehydrophilic polyoxyethylene chain is attached will become a ##STR2##group. Such hydrophilic polyoxyethylene chain is generally expressed interms of an average number of moles of ethylene oxide.

Illustrative examples of biodegradable nonionic surfactants of the typesdefined in the above formula are those consisting of a mixture ofethoxylates of from 11 to 15 carbon atoms in the aliphatic hydrophobicchain, and which have an average of 3, 5, 7, 9 and 12 moles of ethyleneoxide, respectively, as the hydrophil.

Materials corresponding to these five examples of biodegradable nonionicsurfactants are marketed, respectively as:

    ______________________________________                                               Tergitol  15-S-3                                                              "         15-S-5                                                              "         15-S-7                                                              "         15-S-9                                                              "         15-S-12                                                      ______________________________________                                    

In each case of the Tergitol S series of surfactants listed above, thenumber to the left of the "S" indicates a hydrophobic aliphatic chain offrom 11 to 15 carbon atoms derived from a mixture of alcohols on C₁₁ toC₁₅ backbone chains, and the number to the right of the "S" designatesthe average number of moles of ethylene oxide as the hydrophil. Thus forexample, Tergitol 15-S-5 is a mixture of linear aliphatic alcohols inthe C₁₁ to C₁₅ range ethoxylated with an average of 5 moles of ethyleneoxide. All of these commercially marketed Tergitol S series ofsurfactants are water soluble except for Tergitol 15-S-3, which isessentially water insoluble. Mixtures of these materials can also beemployed in providing the dye penetrant of the invention, such as amixture of the above Tergitols 15-S-5 and 15-S-3; a mixture of 15-S-3and 15-S-9; and a mixture of 15-S-5 and 15-S-9.

The above preferred class of nonionic biodegradable surfactants employedas carrier or vehicle for the dye of the penetrant solution according tothe invention, are prepared by reacting an alcohol or mixture ofalcohols, with the desired proportion of ethylene oxide, in the presenceof an alkaline catalyst, such as potassium hydroxide. The ethylene oxidemay be added to the alcohol or mixture of alcohols in one continuousstep or it may be added in several steps. The products thus producedpossess random distribution of oxyethylene groups, as noted above.

Another process for preparing the above nonionic surfactants in the formof ethoxylates of linear secondary aliphatic alcohols, is described inU.S. Pat. No. 2,870,220.

Although Tergitol 15-S-3 is essentially water insoluble and is usuallyemployed in combination with the other members of the Tergitol S seriesnoted above, such as Tergitol 15-S-5, dye penetrant compositionsaccording to the invention containing Tergitol 15-S-3 alone, can beemployed. However, Tergitol 15-S-3 has its greatest utility forproduction of dye penetrants having high sensitivity according to theinvention, when employed in combination with the other water washableand water soluble Tergitols such as Tergitol 15-S-5 and Tergitol 15-S-9.Also, particularly effective dye penetrants are provided according tothe invention employing a combination or mixture of the above Tergitols15-S-5 and 15-S-9, and to which there can be added optionally Tergitol15-S-3, as described in my above copending application Ser. No. 521,730.

The incorporation of the glycol monobutyl ether into the dye penetrantcontaining for example the above Tergitol 15-S-3, substantially improvesthe water washability of the resulting dye penetrant, employing suchsurfactant, which as noted above is essentially water insoluble.

Any suitable dye generally employed in dye penetrant compositions can beincorporated into the nonionic oxyalkylated alcohol surfactantsdescribed above for producing the dye penetrant compositions employed inthe invention process. Preferably, however, a fluorescent dye isemployed for this purpose. The ethoxylated surfactant vehicle for thedye is compatible therewith and has the ability to dissolve either smallor relatively large amounts of the dye and to hold a high concentrationof dye in solution while providing good resolution and clarity of thedye trace in the cracks and flaws.

As previously noted, the dye penetrant solution employed according tothe invention preferably contains a fluorescent dye. Various types offluorescent dyes can be employed including for example the dye marketedas Fluorol 7GA as well as other fluorescent dyes such as those marketedas Calcofluor Yellow, Azosol Brilliant Yellow 6GF; Rhodanine B,Rhodanine 6 GDN, Calcofluor White RW, Blancophor White AW, Auramine andEosine G, and water soluble fluorescent dyes such as Blancophor FFG.

The dye penetrant composition employed according to the inventionalternatively can contain non-fluorescent or daylight type dyes such asazo type dyes, e.g., xyleneazobeta-naphthol, Mefford No. 322 dye,believed to be o-tolueneazoxyleneazo-beta-naphthol, and the azo dyesmarketed as Oil Red "O" and Sudan Red. These dyes conveniently can beemployed where daylight or white light is only available, andparticularly where the surface of the body to be detected containsrelatively gross cracks. However, it is preferred to employ fluorescentdyes having greater sensitivity or detectability as result of the highcontrast obtained by the fluorescent indications.

The amount of dye which is incorporated into the ethoxylated alcoholsurfactant or carrier to produce the dye penetrant composition of theinvention, can range from about 0.1 to 15, preferably about 0.5 to about10, parts of the dye, or mixtures thereof, per 100 parts of theethoxylated alcohol surfactant, by weight. In preparing the dyepenetrant composition employed according to the invention, the dye issimply added to the ethoxylated alcohol carrier, in the desiredproportion. The resulting dye penetrant composition has both high andlow temperature stability.

The amount of the glycol monobutyl ether incorporated into the dyepenetrant composition hereof containing ethoxylated alcohol surfactantand dye, generally ranges from about 10 to about 150%, preferably fromabout 20 to about 100%, by volume of the initial dye penetrantcomposition, that is, the sum of the ethoxylated alcohol surfactant anddye. If more than about 150% by volume of the glycol monobutyl ethercomponent based on the sum of the thoxylated alcohol surfactant and dyeis employed, the sensitivity of the dye penetrant composition commencesto decay, probably due to the fact that at such high concentration ofthe glycol monobutyl ether component, the glycol ether solvent carrieswith it some of the dye remaining in the cracks and flaws of the part.The use of less than 10% by volume of the other components, of theglycol monobutyl ether substantially reduces the advantages of thinningwhich are sought to be obtained by incorporation of the glycol monobutylether component in the dye penetrant composition.

In carrying out the invention process, if necessary, the part or surfaceto be inspected first can be suitably prepared as for example bysuitably cleaning and drying the part.

The liquid dye penetrant composition containing the glycol monobutylether is applied to the test specimen, for example by dipping same intoa bath of the penetrant, or the penetrant can be poured or sprayed ontothe surface of the test specimen. Preferably the dye penetrantcomposition hereof is sprayed on the specimen surface, such sprayingbeing aided by use of the glycol monobutyl ether extender. The dyepenetrant composition is maintained on the surface of the test body orspecimen for a period sufficient to permit the composition to penetratethe cracks and imperfections in the part surface, e.g. for about 1 toabout 5 minutes.

The above-noted water wash is then applied for preferentially removingthe glycol monobutyl ether from the dye penetrant, the excess remainingdye penetrant composition, stripped of the glycol monobutyl ether, thenimmediately being removed or washed off the surface of the part beingtested, as noted above, in the same wash operation, without beingremoved from the openings of the surface cracks or flaws. This washingoperation can be accomplished by any suitable means such as byapplication of a plain water spray or a sprayed mixture of air andwater, leaving a portion of the dye penetrant free of glycol monobutylether remaining in the cracks and defects of the part.

As previously noted, the glycol monobutyl ether has the ability ofimmediately abandoning the penetrant solution upon contact with water.This is due to the property of such glycol ether of having preferentialaffinity for water, and thus being preferentially removed first with thewater wash, while momentarily leaving the dye penetrant containing dyeand dye vehicle uniformly distributed over the surface of the part, andwhich is then finally removed by the water wash. Such immediate andmomentary disassociation and removal of the glycol monobutyl ether fromthe basic penetrant formulation upon application of water, thus permitsthe remaining dye penetrant to have the same sensitivity and brightnessproperties as the initially formulated penetrant composition, prior toincorporation of such glycol ether, with the advantages that the removalof such nonvolatile solvent is accomplished rapidly by means of a waterwash, followed immediately by removal of the remaining dye penetrantuniformly distributed over the surface of the part, in the same waterwash, without the necessity of using a volatile type solvent for thispurpose. When employing volatile type solvents for thinning dyepenetrants, as in the prior art, it is necessary to wait for completeevaporation of the solvent and for the remaining penetrant to dry,before removal of remaining dye penetrant. If such volatilesolvent-thinned penetrant is removed by the washing step before itssolvent evaporates, the volatile solvent still present in the remainingpenetrant in the cracks and flaws will affect the sensitivity of the dyepenetrant.

Following washing and removal of glycol monobutyl ether and remainingdye penetrant composition from the part surface, followed by drying, thesurface is then viewed under suitable lighting conditions, e.g.ultraviolet or black light when the dye in the dye penetrant is afluorescent dye, to locate any cracks or defects on the surface of thebody, as indicated by colored traces, for example, by fluorescentemissions, from the dye penetrant therein.

If desired, after removal of excess dye penetrant composition and dryingthe part surface, a developer composition can be applied to the partsurface followed by removal of excess developer, as by means of an airblast. The part is then viewed under suitable lighting conditions,employing black light or fluorescent illumination when the dye penetrantcontains a fluorescent dye. For this purpose, a dry powder ornon-aqueous (volatile solvent base) developer composition can beemployed. Preferred developer compositions for use in conjunction withthe dye penetrant composition according to the invention, are thosedescribed in my U.S. Pat. No. 3,803,051, which is a dry powder developercontaining fumed alumina, fumed silica, fumed titanium dioxide and talc,and in my U.S. Pat. No. 3,748,469, and which is a wet non-aqueousdeveloper composition consisting essentially of isopropyl alcohol, talcand glycol monobutyl ether. The descriptions of such developercompositions contained in the above patents are incorporated herein byreference.

The following are examples of practice of the invention.

EXAMPLE 1

The following liquid dye penetrant was prepared and designated dyepenetrant A:

    ______________________________________                                        COMPONENTS           Parts by Weight                                          ______________________________________                                        Tergitol 15-S-5      100                                                      Calcofluor White RW   5                                                       Fluorol 7 G A        1.5                                                      ______________________________________                                    

To the above dye penetrant A was added glycol monobutyl ether in anamount of 10% by volume of composition A. The resulting dye penetrantcomposition containing glycol monobutyl ether is designated compositionB.

The fluorescent dye penetrant composition B above was applied as byspraying, to one-half the surface of a chromium-plated brass test panelcontaining cracks 0.00002 to 0.0001 inch in width, closely distributedover its entire surface. A water wash was then applied by an air-waterrinser over the coating of dye penetrant composition B on the testpanel, causing preferential removal of the glycol monobutyl ether fromthe dye penetrant composition, and also instantaneously washingremaining dye penetrant, now free of glycol monobutyl ether, andcorresponding to the initial dye penetrant A, from the surface of thetest panel. The test panel was then dried. The dye penetrant washed fromthe surface of the panel was biodegradable.

The other half of the test panel surface was sprayed with dye penetrantA above, initially containing no glycol monobutyl ether. The excess dyepenetrant was then removed by spraying a mixture of air and water overthe panel surface. The test panel was then dried.

Both halves of the test panel surface were covered with a powderdeveloper having the following composition, according to my above U.S.Pat. No. 3,083,051.

    ______________________________________                                        COMPONENTS         Percent by Weight                                          ______________________________________                                        Talc               52                                                         Alumina            35                                                         Silica              4                                                         TiO.sub.2           9                                                         ______________________________________                                    

The above developer was permitted to dwell over the surface of the testpanel for a period of about 2 minutes.

Excess developer composition was then carefully removed from the surfaceof the test panel by means of a gentle air blast.

Inspection of the two penetrant treated surfaces of the test panel underultraviolet or fluorescent light, revealed fluorescent indications fromnumerous readily defined microcracks therein, the fluorescentindications on both sides of the test panel being in substantiallyequivalent concentration, with substantially the same brightness andsensitivity or optical intensity on both sides of the test panel.

From the above, it is seen that the glycol monobutyl ether, whileserving as an extender and temporary carrier for the dye penetrant A,can be readily removed from the dye penetrant, so that the resulting dyepenetrant has substantially the same fluorescent brightness andsensitivity characteristics as the dye penetrant A initially applied, inthe absence of the glycol monobutyl ether extender. In addition, the dyepenetrant solution washed from the first half of the test panel surfaceto which the composition B containing glycol monobutyl ether wasapplied, was biodegradable.

EXAMPLE 2

The procedure of Example 1 was repeated employing compositionscorresponding to composition B of Example 1, but employing,respectively, proportions of glycol monobutyl ether to composition A,commencing with a proportion of 20% of glycol monobutyl ether tocomposition A, and in increments of 10% by volume up to a compositioncontaining 150% of glycol monobutyl ether, by volume, to composition A.

Results in each case were obtained similar to the results of Example 1.

EXAMPLE 3

The procedure of Example 1 was repeated but employing the following dyepenetrant composition, designated composition C:

    ______________________________________                                        COMPONENTS           Parts by Weight                                          ______________________________________                                        Tergitol 15-S-5      75                                                       Tergitol 15-S-9      25                                                       Calcofluor White RW  2.5                                                      Fluorol 7 G A        0.75                                                     ______________________________________                                    

To the above dye penetrant composition C was added glycol monobutylether in an amount of 50% by volume of composition C. The resulting dyepenetrant composition containing glycol monobutyl ether was designatedcomposition D.

The dye penetrant composition D and dye penetrant composition C wereapplied to respective half sides or surfaces of an aluminum test panelhaving microcracks within the range of those noted for the test panel inExample 1.

In the case of the half panel surface coated with dye penetrantcomposition D, the air-water spray preferentially removed glycolmonobutyl ether, followed almost instantaneously by removal of theremaining dye penetrant from the surface of the panel. The dye penetrantthus removed was biodegradable.

Following removal of remaining dye penetrant from each of the two halfsurfaces of the panel, and drying, both halves of the test panelsurfaces to which penetrant composition D and penetrant C were applied,were covered with a powder developer of the type described in Example 1,following which excess developer composition was removed as described inExample 1.

Both halves of the test panel were then placed under fluorescentillumination and it was observed that both surfaces of the test paneldisclosed fluorescent indications from the microcracks in the testpanel, showing substantially the same concentration of numerousmicrocracks in both halves of the panel, with substantiallycorresponding brightness and definition in both half surfaces of thepanel.

EXAMPLE 4

The procedure of Example 1 was substantially repeated except that a testpanel was employed containing relatively gross cracks substantiallygreater than 0.0001 inch in width, and no developer composition wasemployed.

When the test panel was placed under fluorescent illumination, both halfsurfaces of the panel showed substantially the same concentration offluorescent dye traces and of substantially the same brightness andresolution, detecting the location and size of the microcracks, andagain indicating substantially the same sensitivity for dye penetrantcomposition B following removal of the glycol monobutyl ether, as in thecase of dye penetrant A which initially contained no such glycol ethercomponent.

EXAMPLE 5

The procedure of Example 1 was repeated except that dye penetrant A wasreplaced by a dye penetrant comprising 10 parts of Tergitol 15-B-5 and 1part of daylight visible Oil Red "O" dye, by weight, the resulting dyepenetrant composition designated E, and to such penetrant was addedglycol monobutyl ether in amount about 60% by volume of composition E,the resulting composition designated F.

The compositions E and F were applied to half surfaces of an aluminumpanel containing gross cracks and respective half surfaces of the testpanel were processed as in the case of compositions A and B in Example1.

Both half surfaces of the panel were then exposed to ordinary daylight,showing the same good clarity and definition, and substantially the samebrightness, of the dye trace patterns for the cracks in both halfsurfaces of the panel.

From the foregoing, it is seen that the invention provides an effectivebiodegradable substantially non-flammable and non-toxic water washabledye penetrant composition thinned or extended by incorporation of glycolmonobutyl ether, facilitating spraying of the composition on a test partand permitting rapid initial removal of the extender, with practicallyinstantaneous removal of remaining dye penetrant in a single washoperation, the washed penetrant being biodegradable, followed by furtherprocessing of the dye penetrant coating as desired in the conventionalmanner for viewing under suitable, e.g. fluorescent, lighting conditionsto obtain the same sensitivity and brilliance of dye traces as in thecase of the same dye penetrant in the absence of glycol monobutyl ether,and avoiding the use of volatile extenders and thinners.

Since various changes and modifications of the invention will occur toand can be made readily by those skilled in the art without departingfrom the invention concept, the invention is not to be taken as limitedexcept by the scope of the appended claims.

I claim:
 1. A water washable biodegradable liquid dye penetrantcomposition for use in non-destructive testing for detecting cracks andflaws in the surface of an object, which consists essentially of (1) asingle biodegradable nonionic surfactant which consists essentially ofethoxylates of linear secondary aliphatic alcohols, with the hydroxylgroups randomly distributed, the liner aliphatic portion of saidalcohols being a mixture of alkyl chains containing in the range from 10to 17 carbon atoms, and containing an average of from 3 to 12 moles ofethylene oxide, (2) a dye soluble in said surfactant and (3) glycolmonobutyl ether as extender.
 2. A dye penetrant composition as definedin claim 1, wherein said surfactant consists of ethoxylates of a mixtureof alcohols having the formula:where n is in the range from 9 to 13 andm is an average of 3 to
 12. 3. A dye penetrant composition as defined inclaim 2, wherein said surfactant is selected from the group consistingof said ethoxylates of said mixture of alcohols, wherein n ranges from 9to 13, and m is an averge of 3, 5, 7, 9, or
 12. 4. A dye penetrantcomposition as defined in claim 1, wherein said dye is a fluorescentdye.
 5. A dye penetrant composition as defined in claim 2, wherein saiddye is a fluorescent dye and said dye is present in said composition inan amount ranging from about 0.1 to 15 parts, per 100 parts, by weightof said surfactant.
 6. A dye penetrant composition as defined in claim1, said glycol monobutyl ether being present in a proportion rangingfrom about 10 to about 150% of the sum of said surfactant and said dye,by volume.
 7. A dye penetrant composition as defined in claim 4, saidglycol monobutyl ether being present in a proportion ranging from about10 to about 150% of the sum of said surfactant and said dye, by volume.8. A dye penetrant composition as defined in claim 5, said glycolmonobutyl ether being present in a proportion ranging from about 10 toabout 150% of the sum of said surfactant and said dye, by volume.
 9. Adye penetrant composition as defined in claim 2, said glycol monobutylether being present in a proportion ranging from about 20 to about 100%of the sum of said surfactant and said dye, by volume.
 10. A dyepenetrant composition as defined in claim 3, said glycol monobutyl etherbeing present in a proportion ranging from about 20 to about 100% of thesum of said surfactant and said dye, by volume.
 11. A dye penetrantcomposition as defined in claim 5, said glycol monobutyl ether beingpresent in a proportion ranging from about 20 to about 100% of the sumof said surfactant and said dye, by volume.
 12. A dye penetrantcomposition as defined in claim 3, wherein m in said surfactant is anaverage of
 5. 13. A dye penetrant composition as defined in claim 12,wherein said dye is a fluorescent dye and said dye is present in saidcomposition in an amount ranging from about 0.1 to 15 parts, per 100parts, by weight of said surfactant, and said glycol monobutyl etherbeing present in a proportion ranging from about 10 to about 150% of thesum of said surfactant and said dye, by volume.
 14. A dye penetrantcomposition as defined in claim 3, employing a combination of saidbiodegradable nonionic surfactants wherein m is one of said surfactantsis an average of 5 and m in another of said surfactants is an average of9.
 15. A dye penetrant composition as defined in claim 14, wherein saiddye is a fluorescent dye and said dye is present in said composition inan amount ranging from about 0.1 to 15 parts, per 100 parts, by weightof said surfactant, and said glycol monobutyl ether being present in aproportion ranging from about 10 to about 150% of the sum of saidsurfactant and said dye, by volume.
 16. A dye penetrant composition asdefined in claim 15, said glycol monobutyl ether being present in aproportion ranging from about 20 to about 100% of the sum of saidsurfactant and said dye, by volume.